DUAL BAND ANTENNA FOR MOBILE COMMUNICATIONS

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to antennas, and more particularly, to a dual band antenna for mobile communications.

2. Description of the Related Art

[0002] With the rapid progress of mobile communications, the capacity of existing systems is becoming saturated, and thus, new systems are being developed at new frequencies to enhance capacity. Accordingly, the interrelationship between existing and new systems must be taken into consideration in the design of mobile communications equipment. For mobile communications antennas, major design concerns are power efficiency and effective use of frequency.

[0003] In practice, it is desirable in the Republic of Korea (South Korea) to interlink the existing CDMA (Code Division Multiple Access) system with the new PCS (Personal Communication System) system, in the U.S.A. to interlink the existing AMPS (Advanced Mobile Phone Service) system with the PCS system, and in Europe to interlink the existing GSM (Groupe Speciale Mobile) system with the DCS (Digital Communication System) 1800 system. Generally, a "dual band system" is a system that allows for communications within two different systems at different frequency bands, such as in above examples. It is desirable to manufacture communications equipment capable of operating within dual band systems. Heretofore, each radio telephone terminal in the dual band systems are provided with two separate miniature antennas for two different bands, which results in increased production cost. Also, the use of two antennas for this purpose is an obstacle to the miniaturization of the radio telephone terminal, and results in an inconvenience to the user. For these reasons, it is required to develop a dual band antenna capable of being used for both bands.

[0004] U.S. Patent No. 4,509,056 discloses a multi-frequency antenna employing a tuned sleeve choke. Referring to FIG. 1, an antenna of the type disclosed in that patent is shown. This antenna operates effectively in a system in which the frequency ratio between operating frequencies is 1.25 or higher. The internal conductor 10 connected to coaxial feed line 2 and the sleeve choke 12i act as a radiating element. The feed point of sleeve choke 12i is short-circuited and the other end thereof is open. The lengths of conductor 10 and sleeve choke 12i are designed so as to achieve maximum efficiency at a desired frequency.

[0005] The choke 12i is partially filled with dielectric material 16i that is dimensioned so that the choke forms a quarter wavelength transmission line and prevents coupling between the shell 14i and the extension 10 at the open end of the choke at the highest frequency. At some lower frequency of operation, the choke 12i becomes ineffective as an isolation element and the entire length P of the structure from the ground plane to the end of the conductor, becomes a monopole antenna at the lower resonant frequency.
The coupling between conductor 10 and sleeve choke 12i occurs at the open end of sleeve choke 12i. That is, when the length

the choke acts as a high impedance, whereby the coupling between conductor 10 and sleeve choke 12i is minimal. When

the choke acts as a low impedance, whereby the coupling between conductor 10 and choke 12i is higher. The electrical length of choke 12i can be adjusted by varying the dielectric constant of dielectric material 16i.
The construction consisting of internal and external conductors 10, 14i is regarded as coaxial transmission, and its characteristic impedance is expressed as follows:


where ε_r is dielectric constant, D is the diameter of the external conductor, and d is the diameter of the internal conductor. The input impedance between internal and external conductors 10, 14i is denoted by the following equation:

where γ = α+jβ , α is attenuation factor, β is propagation constant, 1 is length of transmission line, and Z_L is load impedance. In the antenna of FIG. 1, the ground plate 20 and external conductor 14i are structurally adjacent to each other, thereby causing parasitic capacitance which degrades the antenna efficiency. To improve the antenna efficiency, the parasitic capacitance can be decreased. Accordingly, in the construction of FIG. 1, the diameter of external conductor 14i must be reduced for this purpose, which is ultimately the same as the reduction of characteristic impedance of choke 12i according to the above equation (1). That is, such reduction in the characteristic impedance of choke 12i gives rise to a change in the amount of coupling, resulting in a degradation of the antenna's performance.
Thus, to minimally affect the amount of coupling and to keep the characteristic impedance of choke 12i essentially the same as it was previously (i.e., before the diameter of conductor 14i changed), the diameter of internal conductor 10 must be reduced. This results in a reduction in the antenna's bandwidth. Therefore, when the antenna is manufactured in such a manner, the same cannot satisfactorily cover the frequency bandwidth required for the system.
Further, since, the dielectric material is employed to adjust the quantity of coupling, the dielectric constant and the dimension of the dielectric material must be accurately selected for proper coupling.

SUMMARY OF THE INVENTION

[0006] Accordingly, it is the object of the present invention to provide a dual band antenna with improved performance and bandwidth, by minimizing the parasitic capacitance, between a ground plane and an external conductor thereof.

[0007] This object is solved by the invention as claimed in the independent claim. Preferred embodiments are defined by the dependent claims.

[0008] It is an aspect of the present invention to provide a dual band antenna which has a simple and compact structure and high performance.

[0009] It is still another aspect of the present invention to provide a dual band antenna which is inexpensive and convenient to use.

[0010] In an exemplary embodiment of the present invention, a dual band antenna for mobile communications includes a rod-shaped radiating element having a first portion of a predetermined length connected to a coaxial feed line, and a second portion of a specified length integrally extending from the first portion. The coaxial feed line connects to a ground plate, and a first capacitive load connects to the first portion of the radiating element. A choke surrounds the second portion of the radiating element, and has a shorting end connected to a distal end of the second portion and an open end at a proximal end of the second portion. A second capacitive load is connected at the shorting end of the choke. In a higher operating band of the dual band, the input impedance of the choke is high, such that only the first (lower) portion of the radiating element radiates. At a lower operating band of the dual band, the choke's input impedance is lower to allow for radiation from the entire length of the antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 

FIG. 1 is a sectional view of a monopole antenna operating at dual frequencies according to a conventional embodiment of multi-frequency antenna employing tuned sleeve chokes;

FIG. 2 is a sectional view illustrating the construction of a dual band antenna according to an embodiment of the present invention; and

FIGS. 3A and 3B are circuit diagrams illustrating equivalent circuits of the antennas of FIGS. 1 and 2, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0012] An exemplary embodiment of the present invention will now be described more specifically with reference to the drawings attached only be way of example. It is to be noted that like reference numerals and characters used in the accompanying drawings refer to like constituent elements.

[0013] Referring now to FIG. 2, an antenna in accordance with the invention includes a choke 35 formed as a metal pipe, with the lower end of the choke being open. A rod-shaped radiating element 33 is positioned within choke 35, with an upper end of radiating element 33 being connected to an upper end of the choke (short-circuited end). The open circuited end of choke 35 is approximately at a distance L1 from ground plane 20. A lower end of radiating element 33 is connected to internal conductor 8 of coaxial feed line 2. A capacitive load 36 is connected to the short-circuited end portion of choke 35. Another capacitive load 37 is connected to radiating element 33 at a specified distance downward from the open-end of choke 35.

[0014] Capacitive load 36 can be either a coaxial cylinder or a parallel wire or wires. In the embodiment of FIG. 2, capacitive load 36 is symmetrical with respect to radiating element 33; however, it may alternatively be asymmetrical with respect to the radiating element in other embodiments. The provision of capacitive loads 36, 37 permits the overall antenna length to be shorter than the physical length of the well-known quarter-wave monopole antenna.

[0015] Since the impedance of choke 35 (in conjunction with the radiating element 33 inserted therein) changes as a function of frequency, this characteristic can be advantageously used to enable the antenna of FIG. 2 to operated simultaneously in two different frequency bands. For instance, choke 35 can be designed with a length of λ/4 at the center frequency of a high frequency band, e.g., 1, 700-1, 990 MHz such that only the first portion of radiating element 33 radiates in the high band. At a low enough frequency, the entire antenna of length L2 radiates.

[0016] The input impedance Zin at the choke 35 input terminal at the high frequency band is determined in accordance with the above equation (2). Zin can also be expressed by the following equation (3) because the load impedance Z_L is a short-circuit:

[0017] If the attenuation factor α is ignored (i.e., α = 0), Zin is denoted by the following equation (4):


where β is the propagation constant " 2π/λ ".

[0018] By using eqn. (4), the input impedance Zin when 1 = λ/4 can be expressed by the following equation (5):

[0019] As the calculation result above indicates, the input impedance of choke 35 in the higher frequency band becomes almost infinite, whereby only the lower portion (hereinafter referred to as "first portion") of radiating element 33 below the open-end of choke 35 radiates. The remaining portion of radiating element 33, i.e., the portion inserted into choke 35 (hereinafter referred to as the "second portion" of the radiating element) does not radiate when the choke input impedance is very high, which is preferably the case within the higher frequency band. As a result, in the high frequency band, the antenna of FIG. 2 operates as a λ/4 monopole antenna having a length of L1 (assuming that the length L1 is selected to correspond to about λ/4 at a frequency within the higher frequency band). In the lower frequency band of the dual band, the choke 35 input impedance is lower, whereby choke 35 and radiating element 33 are electrically coupled. Thus, in the lower band, the antenna operates as a 1/4 wavelength monopole antenna having a length of L2 (assuming that the length L2 is selected to correspond to about λ/4 at a frequency within the lower frequency band) . As mentioned above, the capacitive loading of loads 36 and 37 will affect the exact lengths selected for L1 and L2.

[0020] In the following discussion, examples are presented, illustrating the variation, as a function of frequency, of the input impedance of choke 35 within the antenna of FIG. 2 for specific frequencies. As a first example, the impedance variation within the PCS frequency band of Korea Telecom is expressed by the following equation 6:


where Fhmin and Fhmax are the minimum and maximum frequencies, respectively, within the band.

[0021] Since the characteristic impedance Zc of choke 35 is governed by the above eqn. (1), the characteristic impedance is calculated by substituting the actual value in eqn. (1), resulting in the following eqn. (7) :

[0022] Therefore, the amount of input impedance variation at frequencies in the above PCS frequency band can be expressed by the following eqn. (8):

[0023] As calculated above, since the input impedance Zin is high, the choke 35 does not operate as a radiating element in the higher frequency band.

[0024] Next, the input impedance Zin at the input terminal of choke 3.5 in the CDMA (800MHz) frequency band is calculated as the following, equation (9):


where Flmin and Flmax are the lowest and highest frequencies, respectively, within the band.

[0025] As a result, in the lower frequency band, the choke 35 and the radiating element 33 are coupled, such that the entire length L2. of the antenna radiates. Thus, if L2 is selected to correspond to a quarter wavelength at a frequency within the lower frequency bandy the antenna acts as a quarter wavelength monopole antenna.

[0026] As illustrated in FIG. 2, since the choke 35 is separated from coaxial feed line 2 and ground plate 20 by a significant distance, e.g., by about the distance corresponding, to λ/4 at the center of the higher frequency band, the effect of parasitic capacitance is thereby reduced. Also, the diameter dl of radiating element 33 can be made larger than the diameter d of the antenna shown in FIG. 1, thereby allowing for a wider operating bandwidth as compared to that prior art antenna.

[0027] With reference now to FIGS. 3A and 3B, there are shown lumped element equivalent circuits for the antennas of FIGS. 1 and 2, respectively..The coupling between radiating element 33 and choke 35 is a function of the shown capacitor and inductor, and the radiating element 33 is divided into first and second portions with the parallel LC resonant circuit in between.

[0028] Since the above-described antenna of the present invention has a broad bandwidth, the same single antenna can be used within a dual band system such as GSM/bECT, GSM/DCS1800, AMPS, or CDMA (824MHz - 894MHz)/PCS systems. In addition, the above-described antenna can be used for dual bands in which the separation between the upper and lower frequency bands is not an integer multiple of 1/4 wavelength. For this case, the antenna can be designed via appropriate selection of lengths for the first and second portions of the radiating element, and tuning can be effected by using appropriate upper and lower capacitance loadings.

[0029] It will be readily appreciated that an antenna manufactured in accordance with the present invention has the advantage of a simple and compact structure with high performance, while being easy to manufacture, inexpensive and convenient to use.

[0030] As described above, although the present invention has been described in detail with reference to the specific embodiment, it must be in no way construed as a limitation of the invention itself, and it will be apparent to those skilled in the art that many changes and modifications may be made thereto without departing from the present invention. Accordingly, the appended claims cover all such changes and modifications which fall within the scope of the present invention.

Claims

1. An antenna comprising:

a radiating element (33) having a lower portion with a proximal end connected to a feed line (2), and an upper portion;

a hollow cylindrical choke (35) surrounding a portion of said radiating element and having a first end electrically connected to said radiating element and a second end which is open;

wherein in a predetermined high operating frequency band, said choke exhibits a high input impedance such that only the lower portion of said radiating elements radiates, and in a predetermined low operating frequency band, said choke exhibits a lower input impedance such that said radiation occurs from an entire length of said antenna including a length of said upper and lower portions of said radiating element,

characterized in that

said portion of said radiating element surrounded by said hollow cylindrical choke is the upper portion of said radiating element reaching the distal end of said radiating element, and

said first end of said hollow cylindrical choke is electrically connected to said distal end of said radiating element.

2. The antenna of claim 1, further comprising a first capacitive load (36) connected at the short-circuited end of the choke and a second capacitive load (37) connected to the lower portion of said radiating element.

3. The antenna of claim 2, wherein said first and second capacitive loads each comprise a horizontal planar portion and an annular vertical portion formed on a circumference of said horizontal planar portion.

4. The antenna of claim 2 or 3, wherein said horizontal planar portion of said first capacitive load is annularly connected to the shorting end of said choke, and said annular vertical portion of the first capacitive load extends downward a pre-established distance towards the lower portion of said radiating element.

5. The antenna of one of claims 2 to 4, wherein at least one of said first and second capacitive loads is shaped as a coaxial cylinder.

6. The antenna of one of claims 2 to 4, wherein said first capacitive load comprises parallel wires.

7. The antenna of one of claims 2 to 4, wherein said second capacitive load comprises parallel wires.

8. The antenna of claim 2, wherein said second capacitive load is constructed so as to be connected to a peripheral surface of said choke and to surround an outer portion of said choke by a specified length.

9. The antenna of one of claims 2 to 8, wherein said feed line comprises a coaxial feed line.

10. The antenna of claim 9, further comprising a ground plane coupled to an outer conductor of said coaxial feed line.

11. The antenna of claim 2, wherein said second capacitive load has a generally cylindrical outer vertical portion and a planar horizontal portion, said vertical portion annularly connects to a periphery of said horizontal portion, and an inner surface of said horizontal portion connects to said radiating element.

12. The antenna of claim 2, wherein said first capacitive load has a generally cylindrical outer vertical portion and a planar horizontal portion, said vertical portion annularly connects to a periphery of said horizontal portion, and an inner surface of said horizontal portion connects to an outer surface of said short-circuited end of said choke.

13. The antenna of one of claims 2 to 12, wherein said second capacitive load is connected to said radiating element at a predetermined distance from said open end of said choke.

14. The antenna of one of claims 1 to 13, wherein said radiating element is shaped as a rod.

15. The antenna of one of claims 1 to 14, being a dual band antenna.

16. The antenna of claim 15, wherein said low operating frequency band is a range of about 82a, MHz-960 MHz, and said relatively high operating frequency band is a range of about 1,710 MHz-1,990 MHz.

17. The antenna of claim 15 or 16, wherein said lower portion has a length of about a quarter wavelength at a center frequency of a high operating frequency band of said dual band, and said upper and lower portions have a combined length of about a quarter wavelength at a frequency within a low operating frequency band of said dual band.

18. The antenna of claim 1 to 17, wherein:

said choke is a metal choke shaped as a hollow pipe.

Ansprüche

1. Antenne, die umfasst:

ein strahlendes Element (33), das einen unteren Abschnitt mit einem proximaien Ende, das mit einer Speiseleitung (2) verbunden ist, und einen oberen Abschnitt hat;

eine hohle zylindrische Drossel (35), die einen Abschnitt des strahlenden Elementes umgibt und ein erstes Ende, das elektrisch mit dem strahlenden Element verbunden ist, sowie ein zweites Ende hat, das offen ist;

wobei in einem vorgegebenen hohen Betriebsfrequenzband die Drossel eine hohe Eingangsimpedanz aufweist, so dass nur der untere Abschnitt des strahlenden Elementes strahlt, und in einem vorgegebenen niedrigen Betriebsfrequenzband die Drossel eine niedrigere Eingangsimpedanz aufweist, so dass die Strahlung über eine gesamte Länge der Antenne einschließlich einer Länge des oberen und des unteren Abschnitts des strahlenden Elementes auftritt,

dadurch gekennzeichnet, dass

der Abschnitt des strahlenden Elementes, der von der hohlen zylindrischen Drossel umgeben ist, der obere Abschnitt des strahlenden Elementes ist, der bis zum distalen Ende des strahlenden Elementes reicht, und

das erste Ende der hohlen zylindrischen Drossel elektrisch mit dem distalen Ende des strahlenden Elementes verbunden ist.

2. Antenne nach Anspruch 1, die des Weiteren eine erste kapazitive Last (36), die mit dem kurzgeschlossenen Ende der Drossel verbunden ist, und eine zweite kapazitive Last (37) umfasst, die mit dem unteren Abschnitt des strahlenden Elementes verbunden ist.

3. Antenne nach Anspruch 2, wobei die erste und die zweite kapazitive Last jeweils einen horizontalen planen Abschnitt und einen ringförmigen vertikalen Abschnitt umfassen, der an einem Umfang des horizontalen planen Abschnitts ausgebildet ist.

4. Antenne nach Anspruch 2 oder 3, wobei der horizontale plane Abschnitt der ersten kapazitiven Last ringförmig mit dem Kurzschlussende der Drossel verbunden ist und sich der ringförmige vertikale Abschnitt der ersten kapazitiven Last um eine vorgegebene Strecke auf den unteren Abschnitt des strahlenden Elementes zu nach unten erstreckt.

5. Antenne nach einem der Ansprüche 2 bis 4, wobei wenigstens eine von der ersten und der zweiten kapazitiven Last als ein koaxialer Zylinder geformt ist.

6. Antenne nach einem der Ansprüche 2 bis 4, wobei die erste kapazitive Last parallele Drähte umfasst.

7. Antenne nach einem der Ansprüche 2 bis 4, wobei die zweite kapazitive Last parallele Drähte umfasst.

8. Antenne nach Anspruch 2, wobei die zweite kapazitive Last so aufgebaut ist, dass sie mit einer Randfläche der Drossel verbunden ist und einen äußeren Abschnitt der Drossel um eine vorgegebene Länge umgibt.

9. Antenne nach einem der Ansprüche 2 bis 8, wobei die Speiseleitung eine koaxiale Speiseleitung umfasst.

10. Antenne nach Anspruch 9, die des Weiteren eine Bodenfläche (ground plane) umfasst, die mit einem äußeren Leiter der koaxialen Speiseleitung gekoppelt ist.

11. Antenne nach Anspruch 2, wobei die zweite kapazitive Last einen im Allgemeinen zylindrischen äußeren vertikalen Abschnitt und einen planen horizontalen Abschnitt hat, der vertikale Abschnitt ringförmig mit einem Rand des horizontalen Abschnitts verbunden ist, und eine Innenfläche des horizontalen Abschnitts mit dem strahlenden Element verbunden ist.

12. Antenne nach Anspruch 2, wobei die erste kapazitive Last einen im Allgemeinen zylindrischen äußeren vertikalen Abschnitt und einen planen horizontalen Abschnitt hat, der vertikale Abschnitt ringförmig mit einem Rand des horizontalen Abschnitts verbunden ist und eine Innenfläche des horizontalen Abschnitts mit einer Außenfläche des kurzgeschlossenen Endes der Drossel verbunden ist.

13. Antenne nach einem der Ansprüche 2 bis 12, wobei die zweite kapazitive Last mit dem strahlenden Element in einem vorgegebenen Abstand zu dem offenen Ende der Drossel verbunden ist.

14. Antenne nach einem der Ansprüche 1 bis 13, wobei das strahlende Element als ein Stab geformt ist.

15. Antenne nach einem der Ansprüche 1 bis 14, die eine Zweibandantenne ist.

16. Antenne nach Anspruch 15, wobei das niedrige Betriebsfrequenzband ein Bereich von ungefähr 824 MHz - 960 MHz ist und das relativ hohe Betriebsfrequenzband ein Bereich von ungefähr 1710 MHz - 1990 MHz ist.

17. Antenne nach Anspruch 15 oder 16, wobei der untere Abschnitt eine Länge von ungefähr einer Viertelwellenlänge bei einer Mittenfrequenz eines hohen Betriebsfrequenzbandes des Zweifachbandes hat und der obere sowie der untere Abschnitt eine gemeinsame Länge von ungefähr einer Viertelwellenlänge einer Frequenz innerhalb eines niedrigen Betriebsfrequenzbandes des Zweifachbandes haben.

18. Antenne nach Anspruch 1 bis 17, wobei:

die Drossel eine Metall-Drossel ist, die als ein hohles Rohr geformt ist.

Revendications

1. Antenne comprenant :

un élément rayonnant (33) possédant une partie inférieure, dont l'extrémité proximale est reliée à une ligne d'alimentation (2), et une partie supérieure,

une pièce de garde cylindrique creuse (35) entourant une partie dudit élément rayonnant et ayant une première extrémité connectée électriquement audit élément rayonnant et une seconde extrémité qui est ouverte ;

dans laquelle, dans une bande prédéterminée de hautes fréquences de fonctionnement, ladite pièce de garde présente une haute impédance d'entrée, si bien que seule rayonne la partie inférieure dudit élément rayonnant et, dans une bande prédéterminée de basses fréquences de fonctionnement, ladite pièce de garde présente une plus faible impédance d'entrée, si bien que ledit rayonnement s'opère sur toute la longueur de ladite antenne, y compris la longueur desdites parties supérieure et inférieure dudit élément rayonnant,

caractérisée en ce que

ladite partie dudit élément rayonnant entourée par ladite pièce de garde cylindrique creuse est la partie supérieure dudit élément rayonnant, atteignant l'extrémité distale dudit élément rayonnant, et

ladite première extrémité de ladite pièce de garde cylindrique creuse est électriquement connectée à ladite extrémité distale dudit élément rayonnant.

2. Antenne selon la revendication 1, comprenant en outre une première charge capacitive (36) connectée à l'extrémité court-circuitée de la pièce de garde et une seconde charge capacitive (37) connectée à la partie inférieure dudit élément rayonnant.

3. Antenne selon la revendication 2, dans laquelle lesdites première et seconde charges capacitives comprennent chacune une partie planaire horizontale et une partie annulaire verticale formée à la circonférence de ladite partie planaire horizontale.

4. Antenne selon la revendication 2 ou 3, dans laquelle ladite partie planaire horizontale de ladite première charge capacitive est connectée de manière annulaire à l'extrémité court-circuitée de ladite pièce de garde et ladite partie annulaire verticale de la première charge capacitive s'étend vers le bas sur une distance prédéterminée, en direction de la partie inférieure dudit élément rayonnant.

5. Antenne selon l'une des revendications 2 à 4, dans laquelle au moins l'une desdites première et seconde charges capacitives prend la forme d'un cylindre coaxial.

6. Antenne selon l'une des revendications 2 à 4, dans laquelle ladite première charge capacitive comprend des fils parallèles.

7. Antenne selon l'une des revendications 2 à 4, dans laquelle ladite seconde charge capacitive comprend des fils parallèles.

8. Antenne selon la revendication 2, dans laquelle ladite seconde charge capacitive est construite de manière à être connectée à une surface périphérique de ladite pièce de garde et à entourer une partie extérieure de ladite pièce de garde, sur une longueur spécifiée.

9. Antenne selon l'une des revendications 2 à 8, dans laquelle ladite ligne d'alimentation consiste en une ligne d'alimentation coaxiale.

10. Antenne selon la revendication 9, comprenant en outre un plan de masse couplé à un conducteur extérieur de ladite ligne coaxiale.

11. Antenne selon la revendication 2, dans laquelle ladite seconde charge capacitive possède une partie verticale extérieure généralement cylindrique et une partie planaire horizontale, ladite partie verticale se connectant de manière annulaire à une périphérie de ladite partie horizontale, et une surface intérieure de ladite partie horizontale se connectant audit élément rayonnant.

12. Antenne selon la revendication 2, dans laquelle ladite première charge capacitive possède une partie verticale extérieure généralement cylindrique et une partie planaire horizontale, ladite partie verticale se connectant de manière annulaire à une périphérie de ladite partie horizontale, et une surface intérieure de ladite partie horizontale se connectant à une surface extérieure de ladite extrémité court-circuitée de ladite pièce de garde.

13. Antenne selon l'une des revendications 2 à 12, dans laquelle ladite seconde charge capacitive est connectée audit élément rayonnant à une distance prédéterminée de ladite extrémité ouverte de ladite pièce de garde.

14. Antenne selon l'une des revendications 1 à 13, dans laquelle ledit élément rayonnant prend la forme d'une tige.

15. Antenne selon l'une des revendications 1 à 14, qui est une antenne bibande.

16. Antenne selon la revendication 15, dans laquelle ladite bande de basses fréquences de fonctionnement est une plage d'environ 824 MHz à 960 MHz et ladite bande de hautes fréquences de fonctionnement est une plage d'environ 1710 MHz à 1990 MHz.

17. Antenne selon la revendication 15 ou 16, dans laquelle ladite partie inférieure a une longueur d'environ un quart d'onde à une fréquence centrale d'une bande de hautes fréquences de fonctionnement sur ladite double bande et lesdites parties supérieure et inférieure ont une longueur combinée d'environ un quart d'onde à une fréquence située dans une bande de basses fréquences de fonctionnement sur ladite double bande.

18. Antenne selon l'une des revendications 1 à 17, dans laquelle ladite pièce de garde est une pièce de garde métallique ayant la forme d'un tube creux.

Drawing